Chlorophyll degradation and carotenoid biosynthetic pathways: Gene expression and pigment content in broccoli during yellowing.

Broccoli undergoes yellowing in unfavorable conditions, thereby diminishing the sensory quality and commodity value. This study aimed to investigate systematically cellular and/or biomolecular changes involved in broccoli yellowing by analyzing changes in microstructural integrity, pigment content, and gene expression. On day-5 of storage at 20 °C, the buds turned yellow without blooming and showed structural damage; ultrastructural analysis revealed plastid transformation and abnormal chloroplast development. Genes regulating pigment content and chloroplast structure directly were identified. More specifically, BoCAO and BoNYC1 regulated chlorophyll turnover, affecting chlorophyll a and b contents. Changes in the ß-cryptoxanthin content were influenced by the combined action of up- (BoHYD) and downstream (BoZEP) genes. BoZEP and BoVDE were activated after cold-temperature induction. High BoHO1 expression delayed yellowing at low temperature, inducing BoZEP expression. Color intensity correlated significantly with the chlorophyll b, ß-cryptoxanthin, and ß-carotene contents, which were associated with increased yellowing of plant tissues.

The high content of ß-carotene present in orange-pulp fruits of Carica papaya L. is not correlated with a high expression of the CpLCY-ß2 gene.

We investigated the transcriptional regulation of six genes involved in carotenoid biosynthesis, together with the carotenoid accumulation during postharvest ripening of three different papaya genotypes of contrasting pulp color. Red-pulp genotype (RPG) showed the lowest content of yellow pigments (YP), such as ß-cryptoxanthin, zeaxanthin, and violaxanthin, together with the lowest relative expression levels (REL) of CpLCY-ß2 and CpCHX-ß genes. On the contrary, the yellow-pulp genotype (YPG) showed the highest content of YP and the highest REL of CpLCY-ß2 and CpCHX-ß genes. Interestingly, the orange-pulp genotype (OPG) showed intermediate content of YP and intermediate REL of CpLCY-ß2 and CpCHX-ß genes. The highest content of ß-carotene shown by OPG despite having an intermediate REL of the CpLCY-ß2 genes, suggests a post-transcriptional regulation. Thus, the transcriptional level of the genes, directing the carotenoid biosynthesis pathway, can partially explain the accumulation of carotenoids during the postharvest ripening in C. papaya genotypes of contrasting pulp color.